Study on fabrication of heterostructures based on InN, GaN and alloys and applications for HFET

在本研究计画中，我们的目标是发展以氮化铟、氮化镓及其合金为基底的异质结场效电晶体的基础技术。我们研究了等离子体激发分子束外延生长高质量InN和InGaN晶体以及基于这些材料的异质结的制备。本项目取得的主要成果概括如下：1.在蓝宝石衬底上生长InN薄膜时，通过优化氮化、低温生长缓冲层、生长温度等生长条件，成功地生长出了具有高质量叠层和优良电学性能的InN单晶.基于系统的结构和光学特性的研究，使用TEM，XRD，拉曼散射，EXAFS，PL和光学吸收，真正的带隙能量的InN与理想的纤锌矿结构被发现是约0.65 eV。通过简单的氮化和AlN缓冲层的引入，在Si衬底上成功地生长了InN单晶.采用低温生长的InN缓冲层获得了高质量的无相分离的富In InGaN。还发现InN模板的插入在改善富In InGaN的结晶质量和表面形貌方面是非常有效的。在蓝宝石衬底生长的InN模板上成功制备了InN/InGaN量子阱结构，并首次观察到InN阱层的PL发射.研究了InN的热氧化对InN表面化学性质、结构和光学性质的影响。InN的氧化促进了In_2O_3的形成，并对InN的光学性质产生了显著的影响。MonteCarlo模拟结果表明，InN具有比GaN更高的迁移率和饱和速度，具有很好的HFET应用前景。

In this research project, our aim is to develop fundamental technologies for fabrication of HFET based on InN, GaN and their alloys. We have studied the crystal growth of high quality InN and InGaN using plasma-excited molecular beam epitaxy and the fabrication of heterostructure based on these materials. Principal results obtained in this project are summarized as follows ;1. For the InN growth on sapphire by RF-MBE, single crystalline InN with high quality crystalliniy and excellent electrical properties were successfully grown by optimizing growth condition such as nitridation, low-temperature grown buffer layer, growth temperature etc.2. Based on systematic studies on structural and optical characterizations using TEM, XRD, Raman scattering, EXAFS, PL and optical absorption, true bandgap energy of InN with ideal wurtzite structure is found to be approximately 0.65 eV.3. Single-crystalline InN was successfully grown on Si by introducing brief nitridation and AIN buffer.4. High quality In-rich InGaN without phase separation was obtained by using low-temperature grown InN buffer. It was also found that insertion of the InN template was very effective in improving the crystalline quality and surface morphology of In-rich InGaN.5. InN/InGaN quantum well structures were successfully fabricated on the InN template grown on sapphire, and PL emissions from the InN well layers were observed for the first time.6. Influences of thermal oxidation of InN on the chemical properties of InN surface and structural and optical properties were studied. The oxidation of InN was confirmed to promote the formation of In_2O_3, which had a remarkable influence on optical properties of the InN.7. Monte Carlo simulation of electrical properties of InN with narrow bandgap showed that InN has higher mobility and saturation velocity than GaN, indication excellent potential for HFET application.